This invention pertains to adapters. More specifically, this invention relates to adapters for retaining and moving fixture elements associated with a work fixture.
There is a need in manufacturing operations for durable and reconfigurable workholding fixtures especially for flexible manufacturing operations. The fixtures must be readily and accurately adaptable to hold different workpiece shapes for machining applications or the like. Sometimes the workpieces are similar or related part shapes such as cast aluminum cylinder heads for different engines. In other manufacturing situations the parts may be of unrelated design but requiring similar manufacturing operations. In these varied applications, the fixture reconfiguration or changeover from one part design to another has to be fast enough to meet the productivity requirements of current manufacturing systems.
One innovative fixture utilizes the portability of a flat, very powerful electro-permanent magnetic chuck to provide freedom in position maneuverability and autonomous hydraulic modular elements to provide the automated part support or clamp functions. Such a fixture and modular elements are described in patent application Ser. No. 10/243,860 now U.S. Pat. No. 6,644,637 which is commonly owned by the assignee of the present invention and is herein incorporated by reference. Each autonomous integrated modular clamping or supporting element consists of a hydraulic screw pump, a hydraulic cylinder, such as a typical swing clamp cylinder or a compliant member extended work support cylinder, and a steel base plate. The steel base plate provides a channel for hydraulic fluid flow between the hydraulic screw pump and hydraulic cylinder. The base is made of ferromagnetic material so that it is strongly attracted to a magnetized fixture plate. A NC program can command a simple nut-runner to torque the screw pump to actuate the hydraulic swing clamp or support. By packaging the hydraulic power source alongside with the clamp or support, there is no longer a constraint by any rigid and fixed hydraulic feed lines. The mounting surface area of the base plate has been optimized so that there will be enough magnetic flux to create a sufficiently strong magnetic holding force to secure the modular base plate to the chuck. Moreover, the bottom face of the base plate has a specially prepared surface texture and roughness to further increase the sliding resistance to any slippage between the base plate and the magnetic chuck during machining.
Such a fixture system has the ability to reconfigure a part holding fixture quickly and automatically at a special fixture setup station. The fixture setup station is fashioned similar to a state-of-the-art multi-axis machining center. A xe2x80x9cfixture elementxe2x80x9d storage magazine and a xe2x80x9cfixture elementxe2x80x9d changer could replace the traditional cutting tool storage magazine and the automatic cutting tool changer. The choice of the multi-axis machining center is because of its higher positioning accuracy capability over a robotic system. The end of the machine spindle nose requires a specially designed adapter so that a modular fixture element can be swiftly attached to or released from it. It is an object of this invention to provide such an adapter.
This invention provides an adapter permitting the use of a numerically controlled machine in placing fixture elements on the magnetizible fixture plate described above. The structure of the adapter is described in a following paragraph.
Once such an adapter is provided and in a fixture setup station, the magnetic chuck is brought to the station table, hooked up to a power source, and energized at a reduced magnetization level. A modular fixture element, locating, clamping, or supporting as dictated by the specific part fixture arrangement is gripped; by the fixture element changer from the storage magazine and attached to the spindle nose adapter provided by this invention. The X- and Y- drives of the fixture setup station will move simultaneously so that a precise coordinate position on the flat magnetic chuck is aligned. The fixture element is then brought very close to the surface of the magnetic chuck by the motion of the spindle Z-axis. Once the distance between the fixture element base plate and the magnetic chuck has reached a pre-determined value, the fixture element is released by the spindle nose adapter and automatically attaches itself gently to the magnetic chuck surface by the magnetic attractive force. The pre-selected reduced magnetization level is to ensure the fixture element will not be slamming violently onto the chuck. The fixture setup NC program then initiates the next round of commands to setup the second fixture element, the third element, and so on. After all the modular fixture elements are set up accurately in their respective positions, the magnetic chuck is fully energized so as to hold the modular elements with the designed maximum holding power. The part will be laid on the fixture by an overhead gantry loader or other material handling equipment. The spindle nose adapter will pick up a nut-runner adapter (with a built-in torque limiter) from the storage magazine and actuate the screw pumps in the various supporting and clamping elements in a prescribed sequence. Finally, the magnetic chuck together with its fixture elements and the clamped part is transferred to a designated machining station for processing.
In accordance with a preferred embodiment of this invention an adapter is secured to a rotatable and translatable spindle of a numerically controlled machine tool. The spindle has a tool receiving end and an axis of rotation. The adapter receives a cylindrical post member (such as a screw pump post) of a fixture element for placement on a fixture body. The adapter has a first end having a receptacle for receiving the end of the spindle. The second end of the adapter has a cylindrical socket and is displaced on a longitudinal axis from the first end. The socket is co-axial with the receptacle as well as the spindle that is inserted in the receptacle and sized and shaped to receive the cylindrical post member of a fixture element. A fluid passage is formed in the adapter from the spindle receptacle to the cylindrical socket. The cylindrical socket has an upstream end and a down stream end. A piston is disposed in the upstream end of the socket. The piston is moveable longitudinally within the socket in response to fluid pressure delivered from the spindle through the fluid passage and against the piston. The downstream end of the socket has a circumference with radially inwardly protruding bayonet pins for engaging a circumferential groove provided for such engagement on the cylindrical post member. In a fixture element placing operation, a cylindrical post is inserted into the downstream end of the socket and into engagement with the bayonet pins. The spindle rotates the adapter to lock the pins into detents in the groove. Fluid pressure is then applied to the piston moving it into contact with the cylindrical post member to secure the fixture element for lifting and placing by the NC machine.
The numerically controlled machine is actuated to move its spindle, the adapter and fixture element to place the element on a fixture plate as described above. When the fixture element has been magnetically secured to the plate, the fluid pressure is released and piston no longer is pressed on the top of the screw pump post. The spindle is turned to remove the bayonet pins from the detents and groove on the screw pump surface. The spindle is then lifted from the fixture element carrying with it the adapter and completing one such placing operation.
In a preferred embodiment of the invention, the adapter comprises a compliant member, such as a spring, in a chamber located between the spindle receptacle and the piston portion of the socket member. A purpose of the compliant member is to provide a cushion between the NC machine and its spindle and the fixture member and plate in the event there is an impediment not permitting normal placement of the fixture piece.